1. Field of the Invention
The invention is based on an injector for an injection system for internal combustion engines, having a magnet valve which controls the outflow of fuel from a valve control chamber through an outflow conduit, in which the magnet valve has means for closing the outflow conduit, an armature that is actuatable by an electromagnet and is operatively connected to the means for closing the outflow conduit, a first valve spring and a second valve spring and a first stroke stop.
2. Description of the Prior Art
Two-stage magnet valves for injectors of injection systems are known. With the first opening stage of the magnet valve, it is intended that the nozzle needle of the injection nozzle open slowly, so that the precise metering of small pre-injection quantities is made easier. The second opening stage is used for the main injection. A high opening speed of the nozzle needle is desired.
In a known version of a two-stage magnet valve, the armature of the magnet valve can be urged counter to the opening direction of the magnet valve via two compression springs connected in line. Until a first stroke stop is reached, only a first compression spring acts on the armature counter to the opening direction of the valve; once the armature has passed the first stroke stop, a second compression spring with the same direction of operation additionally acts upon the armature.
A disadvantage of this embodiment is that because of the in-line connection, the structural length of the magnet valve is great. This is problematic especially in modern, compactly designed engines and modern motor vehicles, since the available installation space is as a rule limited. Furthermore, the in-line connection of two springs with the aid of an intermediate part means that the natural frequencies of the magnet valve are relatively low, which can have adverse effects in the operating performance.
A two-stage valve of an injector, which valve is actuated by a piezoelectric actuator, is known from German Patent Disclosure DE-OS 1974 1850. In this magnet valve, once again two valve springs are connected in line, and an intermediate ring is disposed between the two valve springs. This valve again has the disadvantages discussed above.
The object of the invention is to furnish a two-stage magnet valve for an injector that is compact in design and whose operating performance is good at the most various frequencies.
This object is attained in accordance with the invention by an injector for an injection system for internal combustion engines, having a magnet valve which controls the outflow of fuel from a valve control chamber through an outflow conduit, in which the magnet valve has means for closing the outflow conduit, an armature that is actuatable by an electromagnet and is operatively connected to the means for closing the outflow conduit, a first valve spring and a second valve spring and a first stroke stop; in the invention, the first valve spring urges the armature in the closing direction with a greater spring force, and from the closing position of the magnet valve until the first stroke stop is reached, the second valve spring urges the armature in the opening direction with a lesser spring force.
Because of the different directions of action of the first and second valve springs, an especially compact design of the magnet valve is achieved:
For the case where both the first and the second valve springs are compression or tension springs, one valve spring can be disposed on each side of the armature, and thus the length of the valve springs is not added to the structural length of the armature in contributing to the total structural length of the magnet valve. In other words, at least one valve spring can be disposed parallel to and in particular concentrically with the armature, so that the total structural length of the magnet valve is reduced accordingly.
For the case where the first valve spring is a compression spring and the second valve spring is a tension spring, it is even possible for both valve springs to be disposed parallel to and in particular concentrically with the armature, so that the total structural length of the magnet valve is reduced still further.
In addition, in the disposition of the valve springs according to the invention, connecting them in line is avoided, which has a favorable effect on the resonance behavior of the magnet valve.
In a variant of the invention, it is provided that the first valve spring is a compression spring fastened between a housing of the injector and the end of the armature remote from the means for closing the outflow conduit; that the Is second valve spring is a compression spring fastened between the housing of the injector and the end of the armature toward the means for closing the outflow conduit, so that a simple construction is achieved simultaneously with only little space requirement on the part of the magnet valve. The small space requirement is due among other factors to the disposition of the second valve spring between means for closing the outflow conduit and the armature. Also in this version, the metering of small pre-injection quantities is made possible despite a high opening speed of the nozzle needle in the main injection.
In another variant of the invention, it is provided that the second valve spring acts upon the armature via a displaceable intermediate ring, and that the travel of the intermediate ring is limited by the first stroke stop, so that the first stroke stop can be defined simply and precisely.
In one version of the invention, the travel of the armature is limited by a second stroke stop, so that the opening of the magnet valve in the main injection is defined with high repeatability.
In a further version of the invention, the means for closing the outflow conduit are operatively connected to the armature via a thrust rod, so that a spatial separation between the means for closing the outflow conduit and the armature is provided. Moreover, this affords more space for the second valve spring.
In a variant of the invention, it is provided that the second valve spring and/or the intermediate ring is disposed concentrically with the thrust rod, so that the space required by the magnet valve of the invention decreases further.
In a supplement to the invention, it is provided that the means for closing the outflow conduit are a ball and a ball seat in the housing, or that a valve head, disposed on the end of the thrust rod remote from the armature, and a complementary valve seat in the housing, so that in a simple way reliable sealing of the outflow conduit is accomplished.
One version of the invention provides that the injection system is a common rail injection system, so that the advantages according to the invention are extended to these injection systems as well.